1. Field of the Invention
The present invention relates generally to electronic devices, and more particularly to digital camera modules. Even more particularly, the present invention relates to a system for focusing a digital camera module that prevents debris and particulate matter produced by the focusing process from contaminating the sensor array of an image capture device.
2. Description of the Background Art
Digital camera modules are currently being incorporated into a variety of electronic devices. Such camera hosting devices include, but are not limited to, cellular telephones, personal data assistants (PDAs), and computers. The demand for digital camera modules continues to grow as the ability to incorporate the camera modules into host devices expands. Therefore, one design goal of digital camera modules is to make them as small as possible so that they will fit into an electronic device without substantially increasing the overall size of the device. Means for achieving this goal must, of course, preserve the quality of the image captured by the camera modules.
Such digital camera modules typically include a substrate, an image capture device, a housing, and a lens unit. The substrate is typically a printed circuit board (PCB) that includes circuitry to facilitate data exchange between the image capture device and the host device. The image capture device is mounted and electrically coupled to the circuitry of the PCB. The housing is then mounted on the PCB over the image capture device. The housing includes an opening that receives and centers the lens unit with respect the image capture device. Typically, the opening includes a set of threads and the lens unit includes a complementary set of threads that facilitate the factory focusing of the camera module. During a factory focus operation, for example, focusing equipment rotates the lens unit with respect to the housing, which adjusts the distance between the lens unit and the image capture device. When the lens unit is properly focused, it is fixed in position with respect to the housing with an adhesive, a thermal weld, or the like.
Although camera modules that are focused via thread sets provide for relatively accurate focal adjustments, they still have disadvantages. For example, as the lens unit is rotated within the housing, sliding friction between threads creates particulate debris that could easily contaminate the image sensor and/or other optical components (e.g., infra-red filters, protective covers, other lenses, etc.). Consequently, these contaminants accumulate and noticeably degrade the quality of images captured by, for example, blocking light to the image sensor.
It should be noted that although threaded components are used here as an example, other types of focusing components can similarly produce particulate debris that reduces the quality of the captured images. For example, U.S. Pat. No. 6,426,839 issued to Dou et al. discloses a camera module including a plurality of ramps formed directly on a stationary lens located inside the camera module. A rotatable lens carrier (having a separate lens) includes a plurality of legs that engage the ramped surfaces of the stationary lens. Rotating the lens carrier causes the legs of the lens carrier to move up or down the ramped surfaces of the lens, thereby moving the second lens closer to or further from the stationary lens, depending on the direction of rotation. Because the legs of the lens carrier slide over the ramped surfaces of the stationary lens, particulate debris can still be produced and collect on the imaging components of the camera module.
In addition to particulate debris produced by friction, ramped housings are also susceptible to other contaminants. For example, adhesives used to fix lens units to housings can easily run down into the camera module and contaminate the imaging components. Ramped modules are particularly susceptible to fluid contamination because the interface between the lens unit and the housing is typically not as tight as that of threaded camera modules. Generally, the walls of the lens unit and the housing are smooth, as opposed to having threads formed thereon. In addition to providing a path for contaminant entry, the loose fit between the lens unit and the housing can allow the lens barrel to fall out of the housing during steps of the manufacturing process that occur prior to fixing the lens unit to the housing, thereby reducing yield.
In efforts to minimize the accumulation of such contaminants, manufacturers have employed contaminant collecting surfaces within camera modules. For example, U.S. 2006/0103953 (Lee et al.) discloses a camera module that includes a particle collecting groove defined within the housing. In particular, the groove is formed around the peripheral surface of the light receiving aperture of the housing. The groove collects some the debris before it can reach the image sensor or other optical components within the camera module.
Although the groove formed on the camera module disclosed in U.S.2006/0103953 reduces the amount of debris that collects on the image sensor, there are still some disadvantages. For example, debris is still free to move out of the groove because the groove is not entirely isolated. Further, it is unlikely that the camera module will remain upright during use, thus debris is free to fall back out of the groove and obstruct the image sensor and/or optics.
What is needed, therefore, is a camera module design that minimizes the contamination of optical components during assembly and focusing processes. What is also needed is a camera module design that isolates contaminants before they collect on components within the camera module.